1. Field of the Invention
The invention relates to a drive system for a tracked vehicle having means for driving the tracks at different speeds in order to steer the vehicle.
2. Description of the Related Art
It is known in general that, in tracked vehicles, a gearbox is provided in addition to a drive motor, which gearbox additionally also assumes the steering function of the vehicle, by driving the two drive tracks at different speeds. In addition, a plurality of selectable gear stages for forward and reverse travel, brakes and secondary drives for fans, air conditioning, etc. are usually provided on the gearbox.
The gearbox and the motor can be arranged in what is known as an L configuration with respect to one another, that is to say the driving motor is installed longitudinally in the vehicle and therefore lies transversely with respect to the drive axle or with respect to the gearbox which extends from one drive side to the other, that is to say it is installed in the vehicle transversely with respect to the direction of travel. Here, the motor can be arranged on the left or the right in the direction of travel and inputs its drive into the gearbox, for example, via a bevel gear set. In front-wheel drive, the motor is usually situated behind the gearbox in the L configuration and, in rear-wheel drive, ahead of the gearbox, in each case as viewed in the direction of travel. However, the motor can also be installed longitudinally approximately in the vehicle centre, this being referred to as a T configuration.
In what is known as the U configuration, the drive motor is likewise arranged transversely with respect to the direction of travel, parallel to the gearbox or to the drive axle. The motor can be connected to the gearbox, for example, via a spur gear train as transfer gearbox. In a front-wheel-drive vehicle, the motor lies behind the gearbox as viewed in the direction of travel, and the motor lies in front of the gearbox in a vehicle with rear-wheel drive.
However, these drive arrangements require a very large amount of installation space and restrict the utilizable space in the vehicle to a very great extent.
A compact drive arrangement for a Ukrainian T-72 tank is known from the Polish specialist magazine “Nowa Technika Wojskowa”, issue 9/98 page 22. A rear-wheel-drive system is shown, in which the drive motor is arranged transversely between the drive track wheels in the vehicle. The motor inputs its drive in each case into a change-speed gearbox on both sides. For this purpose, an identical gearbox is arranged on both sides of the motor, which gearboxes can be shifted into 5 forward and three reverse gears. The differential speed at the two drive sides for steering the vehicle can be generated only by selecting different gears on the left-hand and right-hand gearbox. Driving around bends with a vehicle of this type requires a large amount of skill from the driver, as the steering radius cannot be set in an infinitely variable manner, but is dependent on the gear ratios. If the bend, which is predefined, for example, by the roadway, does not correspond to a selectable gear radius, the driver has to set the steering radius to be driven in a jolting fashion by rapid changeover of the gear stages.
As a result, a vehicle of this type can be steered only in a very imprecise manner, which results in a safety risk and potential of danger for other traffic participants. For this reason, vehicles of this type are not permitted in public road traffic in many countries.
DE 37 28 171 has disclosed an electromechanical drive system for fully tracked vehicles. In the simplest case, this drive system comprises an electric traction motor which drives both vehicle sides via a central shaft in the same direction and an electric steering motor which drives a zero shaft, the rotational speed of which has a positive effect on one side and a negative effect on the other side. Steering differentials on the left and right add the rotational speeds of the two motors and transmit the summed output to the track wheels. A generator which is driven by an internal combustion engine is provided to generate the electric drive and steering power. The internal combustion engine and the generator can be arranged longitudinally or transversely in the vehicle. The traction motor and/or steering motor can be arranged directly on the drive shaft or next to it, inputting their power into the traction drive or steering drive via bevel gear drives.